1. Field of the Invention
The present invention relates to optical communication apparatuses for transmitting a burst signal, and more specifically, to an optical communication apparatus for transmitting a burst signal by selectively switching signal paths by using a wavelength of the burst optical signal as address information.
2. Description of the Background Art
In one conventional art, a variable wavelength light source is provided as a light source to an optical communication circuit. This variable wavelength light source sends a burst-like optical signal by using the wavelength thereof as address information. Further, a wavelength separator having output terminals each corresponding to a different wavelength is provided on an optical transmission line. With this structure, a high-speed, large-capacity burst optical communication apparatus which is capable of spontaneously and quickly switching signal paths in an optical domain can be achieved. One example of the above-structured optical communication apparatus is disclosed in detail in “Hyperspace Addressed Optical Access Architecture using Active Arrayed Waveguide Gratings, F. Farjady, M. C. Parker, S. D. Walker, OECC98, 15A2-2, 1998.
FIG. 8 is a block diagram showing the structure of an optical communication apparatus according to the above-described background art. In FIG. 8, the optical communication apparatus includes an optical transmitting circuit 510, and first and second optical receiving circuits 5111 and 5112. Between the optical transmitting circuit 510 and the first and second optical receiving circuits 5111 and 5112, bidirectional burst (intermittent) transmission is achieved.
The optical communication apparatus further includes an optical transmission line 505 for transmitting an optical signal, and a wavelength separator 506 for separating the transmitted optical signal into signals which differ in wavelength from each other, and for outputting the signals to the corresponding first or second optical receiving circuits 5111 and 5112.
The optical transmitting circuit 510 includes a baseband signal source 501 for outputting a signal that carries data to be transmitted, and a variable wavelength optical modulation unit 502 for converting the received signal into an optical signal.
The first optical receiving circuit 5111 includes a first optical receiver 5071 for converting the received optical signal into an electrical signal. Similarly, the second optical receiving circuit 5112 includes a second optical receiver 5072 for converting the received optical signal into an electrical signal.
In the optical communication apparatus structured as described above, the baseband signal source 501 intermittently outputs, for example, a baseband digital signal. The variable wavelength optical modulation unit 502 includes a variable wavelength light source for outputting an optical signal of a predetermined wavelength. The variable wavelength optical modulation unit 502 modulates light that is outputted from the above-described variable wavelength light source with the baseband digital signal, and intermittently outputs a burst optical signal.
Here, the wavelength of the light that is outputted from the above-described variable wavelength light source is set to a first wavelength λ1 during a period for transmitting the burst optical signal to the first optical receiver 5071, and is set to a second wavelength λ2 during a period for transmitting the burst optical signal to the second optical receiver 5072.
The wavelength separator 506 is generally implemented as an AWG (Arrayed Wave Guide), and has first and second output ports. The wavelength separator 506 receives the optical signal that is transmitted through the optical transmission line 505, outputs signal components of the first wavelength from the first output port and signal components of the second wavelength from the second output port.
The first optical receiver 5071 is connected to the first output port of the wavelength separator 506, while the second optical receiver 5072 is connected to the second output port of the wavelength separator 506. The first optical receiver 5071 receives the optical signal of the first wavelength λ1 that is intermittently outputted from the first output port of the wavelength separator 506, and then converts the optical signal into an electrical signal so as to be intermittently output therefrom. The second optical receiver 5072 receives the optical signal of the second wavelength λ2 that is intermittently outputted from the second output port of the wavelength separator 506, and then converts the optical signal into an electrical signal so as to be intermittently output therefrom.
As stated above, in the conventional optical communication apparatus, the variable wavelength light source of the variable wavelength optical modulation unit 502 is provided as a light source of the optical transmitting circuit. The optical transmitting circuit sends a burst-like optical signal by using the wavelength thereof as address information. The wavelength separator 506 having output terminals each corresponding to a different wavelength of the output signal is provided on the optical transmission line. With such a structure, a high-speed, large-capacity burst optical communication apparatus which is capable of spontaneous and quick switching among signal transmission paths in an optical domain can be achieved.
However, such a conventional optical communication apparatus is provided only with a single optical transmitting circuit. This optical transmitting circuit uses a baseband digital signal as a transmission signal. Therefore, if a plurality of such optical transmitting circuits are provided and are simultaneously output optical signals to a single optical receiving circuit, a collision occurs among these optical signals, and therefore, these optical signals cannot be respectively detected. As a result, signal transmission cannot be achieved.